Desulfurization of Diesel Fuels via π-Complexation with Nickel(II)-Exchanged X- and Y-Zeolites

Desulfurization of a commercial diesel fuel (297.2 ppmw S) by different nickel(II)-exchanged faujasite zeolites was studied in a fixed-bed adsorber operated at ambient temperature and pressure. The zeolites were prepared by both liquid-phase (LP) and solid-state (SS) ion-exchange (IE) methods. In general, the adsorbents tested for total sulfur adsorption capacity at breakthrough followed the order: Selexsorb CDX (alumina)/Ni(II)-Y (SSIE-500) > Selexsorb CDX (alumina)/Ni(II)-X (LPIE-RT) > Ni(II)-Y (SSIE-500) > Ni(II)-X (LPIE-RT) > Ni(II)-Y (LPIE-135). The best adsorbent, Selexsorb CDX (alumina)/Ni(II)-Y (SSIE-500) [layered bed of 25 wt% activated alumina followed by Ni(II)-Y] is capable of producing 19 cm³ of diesel fuel per gram of adsorbent with a weighted average content of 0.22 ppmw S. These low-sulfur fuels are suitable for fuel cell applications. The sorbents were fully regenerated in one step using air at 350 °C, which simplifies possible implementation for many applications. GC-FPD results showed that the π-complexation sorbents selectively removed highly substituted thiophenes, benzothiophenes, and dibenzothiophenes from diesel, which is not possible using conventional hydrodesulfurization (HDS) reactors or direct sulfur-metal interaction-based zeolites such as Ce(IV)-Y. The high sulfur selectivity and high sulfur capacity of nickel(II)-zeolites were due to π-complexation.